For most individuals, each and every day the plantar tissues of the foot experience thousands of cycles of loading, with each cycle equivalent to their entire bodyweight or more. These tissues cushion and protect the rest of the foot from damage and subsequent problems. In diseases such as diabetes or rheumatoid arthritis, displacement or stiffening of the material properties is common, and this puts these individuals at an increased risk of foot ulceration and related problems. In people with diabetes in particular, foot ulceration is highly prevalent, and leads to almost two thirds of the non-traumatic amputations that occur in the US each year. Our ability to identify feet at-risk of these problems at an early stage, and to protect the tissues using optimized interventions such as therapeutic footwear, is restricted by the lack of tools available to measure the material properties of these tissues in dynamic situations representative of the activities of daily living. The behavior of these tissues is complex, with non-linear and viscoelastic components to their loading response. Current approaches for measuring the material properties of the plantar tissues have tended to involve static indentation rigs, and do not accurately reflect the dynamic behavior of the tissues in the in-shoe environment where the viscoelastic nature of the tissue and the effects of factors including the dynamic stiffness of the nearby muscles play an important role. The proposed experimental work intends to address these problems through the following: Specific Aim 1 - Develop an instrumented shoe that can provide detailed measurements of the dynamic behavior of the plantar tissues of the foot. An ultrasound probe will be embedded within the sole of the shoe to measure tissue strain, and combined with a force transducer to allow simultaneous collection of the forces being imparted onto the probe by the foot. Specific Aim 2 - Validate the instrumented shoe against biplane fluoroscopy. In ten healthy participants and ten participants with diabetes and peripheral neuropathy, measurements of tissue strain beneath the metatarsal heads and calcaneal tuberosity obtained with the prototype footwear will be compared against those from a biplane fluoroscopy system, which is the current gold standard for measuring the dynamic behavior of the bones of the foot. Our group is uniquely positioned to carry out this work, given our experience in using in-shoe ultrasound, and our established biplane fluoroscopy laboratory. The impact of a validated, instrumented shoe for measuring plantar tissue properties could ultimately lead to a step change in our ability to screen for problems, model interventions, and could initiate new treatment strategies aimed at preventing or treating these disorders. The results from this project will motivate and inform the submission of a R01 application to reach these long term goals.